The only unbeaten sides in professional German football meet in the second round of the cup as Borussia Dortmund host second-division Union Berlin. Elsewhere, Schalke travel to Cologne while RB Leipzig host Hoffenheim.On 26 October 2016, over 12,000 Union Berlin supporters traveled west to see their second-division team take Bundesliga giants Borussia Dortmund to penalties in the second round of the cup.

Two years on, the red-clad hordes will be back in the Ruhrgebiet – but their numbers have shrunk to around 8,000. Unlike in 2016, tickets for the away end will still be available outside the Westfalenstadion tomorrow.

The novelty may have worn off for some but the earlier, 18:30 CET kickoff time 500 kilometers (311 miles) from home is also a factor. A request from Dortmund police that fans arrive as early as possible was met with considerable disdain from fans on social media.

Still, Union's form isn't particularly inspiring either. The "Irons" might be third in Bundesliga 2 but they missed the chance to go top on Sunday after a goalless draw against 10-man Dynamo Dresden.

That result followed another 0-0 away at Paderborn, which came on the back of a 1-1 draw with Heidenheim, a game notable for goalkeeper Rafal Gikiewicz's last-minute equalizer. In fact, it's now been a month since an outfield player scored for the Berliners.

"In the second half, I felt like we were scared of scoring," said coach Urs Fischer at fulltime against Dresden. "If we play like that in Dortmund, it could be dangerous – for us."

Dortmund favorites

Dortmund suffered a setback of their own against Hertha Berlin on Saturday but, Salomon Kalou's late penalty aside, the Black and Yellows have been in scintillating form of late, racking up 39 goals in all competitions so far this season. On Wednesday, the best attack in the Bundesliga faces the best defense in Bundesliga 2.

"We know that cup games are never easy," BVB coach Lucien Favre told a press conference on Tuesday, referring to his team's double late-show against Greuther Fürth in Round 1. "Union are compact and very well organized."

After a sensational start to his BVB loan spell, Paco Alcacer has missed the last two games with a thigh injury but was back in training this week. Favre wouldn't be drawn on whether the Spanish striker would be fit to start.

"There will probably be a few changes, but even that's not certain," said the Swiss coach.

Cologne vs. Schalke

This was a regular Bundesliga fixture in recent years but this season it's another cup clash between the Bundesliga and Bundesliga 2. Having finished second last term, Schalke have only won four games so far this season – including a 2-0 win over fourth-tier Schweinfurt in the last round.

Like Union in Dortmund, the Royal Blues travel to Cologne on the back of two consecutive goalless draws against Galatasaray and RB Leipzig, and significant doubts remain over the team's forward line.

No Bundesliga team has scored less and Domenico Tedesco has had his players firing at will from outside the box in training.

"You have periods where no coach in the world can help," said sporting director Christian Heidel in Leipzig. "We all know that the goal is 7.32 meters wide!"

Bundesliga 2 leaders Cologne have had their own goal-scoring problems of late, and frustrations have boiled over after defeat to Duisburg and draws against Kiel and Heidenheim.

"They have every right to express their disappointment," said coach Markus Anfang, referring to whistles from the fans, but he hopes that the cup clash will prove a welcome distraction.

"Schalke are Bundesliga runners-up and Champions League participants," he said. "We want to return to the Bundesliga so we're looking forward to testing ourselves against a top-division side."

Elsewhere in Round 2:

RB Leipzig vs. Hoffenheim
Ralf Rangnick and Julian Nagelsmann have already met once since the confirmation that the latter would be joining the former at the Red Bull Arena next summer, RB Leipzig running out 2-1 winners away at Hoffenheim in the Bundesliga. One will crash out of the cup when the two meet in Leipzig on Wednesday.

Borussia Mönchengladbach vs. Bayer Leverkusen
Two of the most attacking teams in Germany meet for another all-Bundesliga clash, but the two Rhineland clubs have had wildly different fortunes this season. While Dieter Hecking's Foals sit third in the table, Heiko Herrlich's Werkself have endured a difficult start – although they go into this cup meeting with more confidence following Sunday's 6-2 hammering of Werder Bremen.

Hansa Rostock vs. Nuremberg
After disposing of Stuttgart in Round 1, can the third-division side spring another surprise against Nuremberg, who have suffered some heavy defeats on the road this season?

Weiche Flensburg vs. Werder Bremen
Werder look to bounce back from their defeat to Leverkusen as they travel north to fourth-tier Flensburg.

Holstein Kiel vs. Freiburg
One of the longest trips in German football – over 800 kilometers separate Kiel on the Baltic coast from Freiburg on the Swiss border.

Bielefeld vs. Duisburg
Duisburg face a much shorter trip as they travel across the Ruhrgebiet to Bundesliga 2 rivals Bielefeld.